1. Field of the Invention
This invention generally relates to communications circuitry and, more particularly, to a receiver signal strength indicator (RSSI) for measuring the amplitude of a received signal.
2. Description of the Related Art
RSSI circuits are been widely used to detect the strength of an incoming signal in many communication devices. Typically, these circuits use analog circuitry to convert the received voltage to power, and then convert the analog power to a digital value using an analog-to-digital converter (ADC). However, high-speed RSSI devices have been difficult to implement in sub-micron CMOS processes. Conventional RSSI circuits often have a narrow dynamic range, low accuracy, consume high amounts of power, and operate at low speeds. Further, they can be sensitive to fabrication process variations.
In a typical RSSI circuit, input signals first go to a root mean square (RMS) converter, which converts the voltage to the RMS power. Then, the output of RMS converter goes to an ADC. The output of the ADC is a digital representation of the average input signal power, but not the magnitude. If magnitude is required, then some sort of the RMS back-to-magnitude conversion must be performed in the digital domain. Typically, a separate ADC is required for the translation of analog RMS power to a digital presentation. Likewise, a dedicated RMS-to-magnitude converter is required. The RMS converter is difficult to build, because the RMS value is a function of the input signal magnitude, slew rate, and modulation.
It would be advantageous if a simple, low-power, high-speed means existed for directly measuring an analog voltage and converting the analog measurement into a digital value, without the use of RMS conversions.